The morphological observations described in this reuort are part of a biochemical study of progesterone intermediates using sow ovary. This tissue is extensively involved in the production of some steroid hormones. Because the lutein cells are thought to be involved in the synthesis of progesterone and its intermediates and because these cells constitute by size and number the greatest portion of the mass of sow ovary, we confined the morphological investigation to these cells. Sow corpora lutea, fixed with glutaraldehyde and osmium tetroxide were examined by light and electron microscopy.The lutein cells of the sow are large epithelioid cells with oval nuclei and extensive amounts of cytoplasm. Large masses of highly organized smooth endoplasmic reticulum, many oval mitochondria with tubular cristae, and many lipid droplets are present. Only a few profiles of rough endoplasmic reticulum are seen in any one section, and Golgi membranes cannot by distinguished from other smooth membranes. The smooth endoplasmic reticulum is the major membranous organelle in these luteal cells. Microsomal preparations from luteal cells must be very rich in fragments of these smooth membranes. The demonstration of many steroidogenic enzyme systems in microsomal preparations lends strong support to the supposition that these enzyme systems reside in the smooth endoplasmic reticulum.Christensen ('65) has drawn attention to the unusual amount and organization of the smooth endoplasmic reticulum in the interstitial cells of guinea pig testes. This report, an adjunct to a biochemical investigation of the metabolism of progesterone in the sow ovary, deals with some ultrastructural observations of several sow lutein cells.Smooth membranes isolated from the microsomal fraction of sow ovary homogenates by density gradient fractionation (Fouts, '61) were used in studying some intermediary products in the metabolism of progesterone. One of the authors (B.K.) noting the yield of the smooth membrane fraction was greater than expected asked that the purity of the preparation be confirmed by electron microscopy. Subsequent observations of several pellets confirmed the presence of smooth membranes with no contaminating ribosomes, mitochondria1 fragments or nuclei. In addition biochemical checks or purity were performed. The yield of relatively clean smooth membranes in greater quantities than was expected prompted this morphological study on the intact ovary.We consider the extensive mass of highly organized smooth membranes, and ANAT. REC., 161: 77-90.the associated mass of mitochondria and lipid are worthy of description. In addition this report contains a description of a single, highly unusual nucleus that contains an intranuclear membranous system. MATERIALS AND METHODSThe ovaries utilized in this study were collected under the same conditions as those used in the biochemical investigation save that tissues from non-pregnant and pregnant sows were collected separately. At this time only tissues from the non-pregnant animals have been ...

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TWO PLATES (TWELVE FIGURES)Since the early work ('00) of von Winiwarter describing postfetal ovogenesis in rabbit and man, several methods have been employed to test the validity of the concept.By selection of closely graded series of stages, numerous investigators httve introduced evidence of the postpartum formation of ova. These reports have been critically reviewed by Kingsbury ( '38). One of these, Arai ('20), after making extensive counts of the total number of ova present at different ages in rats, concluded that ovogenesis was a continuous process. Allen ( '231, using mouse ovaries produced evidence of the cyclic nature of the process, initiated by mitoses in the germinal epithelium. Bagg and Papanicolaou ( '24) were able to accelerate ovarian activity in guinea pigs by irradiation of the thyroid gland, and found ova, follicle cells, interstitial and lutein cells all were derived from the germinal epithelium. Allen and Creadick ('37) and Allen, Smith and Gardner ('37) by using colchicine in mice more clearly demonstrated mitosis in the germinal epithelium and found convincing evidence of cyclic proliferation of ova from the germinal epithelium, the peak appearing at estrus. Schmidt and Hoffman ( '41) using this technique demonstrated such activity in guinea pig ovaries, only part of which was thought to be concerned in ovogenesis.In another approach Long ('40) reported abundant growth of germinal epithelium in tissue cultures of bits of mouse ovaries. He further demonstrated the formation of ova and follicles from this cultured epithelium.Marx ('41) using rats' ovaries stimulated by injection of gonadotropic extracts, found no evidence of proliferation of ova from the germinal 'A preliminary report of this investigation appeared as an abstract read by title at the meet-